Polyethylene terephthalate polyester resins have found wide spread use in many and varied applications. For example, poly(ethyleneterephthalate) polyester resins find applications in the preparation of many types of films, including photographic film base, in fibers and in the preparation of food containers such as bottles and the like. Processes for recycling scrap polyester have been proposed. Various methods have been disclosed heretofore for the recovery of ethylene glycol and terephthalic acid or derivatives thereof which can be recycled and reused.
U.S. Pat. No. 5,051,528 teaches a process of recovering ethylene glycol and dimethylterephthalate from polyethyleneterephthalate scrap resins by dissolving the scrap polyester resin in oligomers of the same monomers as present in the scrap, passing super-heated methanol through the solution and recovering the ethylene glycol and dimethylterephthalate.
U.S. Pat. No. 4,620,032 teaches an extrusion process for reducing the reaction time in the hydrolysis of polyesters by intimately admixing with molten polyester a depolymerizing agent which is either one of the products resulting from the complete hydrolytic depolymerization of the polyester or water.
U.S. Pat. No. 3,776,945 teaches a process of depolymerizing polyethylene terephthalate waste to obtain dimethylterephthalate and ethylene glycol. The waste is subdivided into dimensions between 4 and 35 mesh and treated at a temperature of 100.degree. C. to 300.degree. C. and the presence of acid catalysts, the proportion of methanol to waste being between 1:1 and 10:1 by weight.
U.S. Pat. No. 3,321,510 relates to a process of decomposing polyethyleneterephthalate by treating with steam at a temperature of from about 200.degree. C. to 450.degree. C. The steam-treated polyethyleneterephthalate is then reduced from a brittle solid product to a powder having a mean particles size of from about 0.0005 to 0.002 millimeters, after which the fine powder is atomized with a gaseous substance including inert gas and methanol vapor to form an aerosol. The aerosol is conducted through a reaction zone at a temperature of 250.degree. C. to 300.degree. C. in the presence of excess methanol vapors.
U.S. Pat. No. 3,037,050 relates to the recovery of terephthalate acid dimethyl ester by treating polyethyleneterephthalate in the form of bulky or lumpy solid masses with super-heated methanol vapor in the presence of any suitable esterification catalyst substantially at atmospheric pressure.
EPA 484,963 teaches a process for recovery of dimethylterephthalate and glycols from polyester scrap that optionally provides a reactor solvent such as a mixture of methylhydrogenterephthalate and dimethyl terephthalate.
It can be seen from the above-recited art that many different techniques have been employed in the recovery of the monomeric constituents from polyesters. Such prior art techniques can either be too costly and inefficient or appropriate primarily for batch-type operation. A disadvantage of prior art processes using methanol is that solid scrap feed directly to the reactor can result in a risk of methanol vapor emission. Extrusion processes can have high operating costs and operate at high energy input levels. Thus, there is a widespread need for a simple, economical, continuous process of treating such polyesters to recover the initial ingredients utilized in the preparation of the polyester polymers or other useful recovery components.